DƯỢC LÍ Goodman & Gilman's The Pharmacological Basis of Therapeutics 12th, 2010

174 third lumbar segment. The axons from these cells are
carried in the anterior (ventral) nerve roots and
synapse, with neurons lying in sympathetic ganglia
outside the cerebrospinal axis. Sympathetic ganglia
are found in three locations: paravertebral, prevertebral,
and terminal.
The 22 pairs of paravertebral sympathetic ganglia
form the lateral chains on either side of the vertebral
column. The ganglia are connected to each other by
nerve trunks and to the spinal nerves by rami communicantes.
The white rami are restricted to the segments
of the thoracolumbar outflow; they carry the preganglionic
myelinated fibers that exit the spinal cord by
the anterior spinal roots. The gray rami arise from the
ganglia and carry postganglionic fibers back to the
spinal nerves for distribution to sweat glands and pilomotor
muscles and to blood vessels of skeletal muscle
and skin. The prevertebral ganglia lie in the abdomen
and the pelvis near the ventral surface of the bony vertebral
column and consist mainly of the celiac (solar),
superior mesenteric, aorticorenal, and inferior mesenteric
ganglia. The terminal ganglia are few in number,
lie near the organs they innervate, and include ganglia
connected with the urinary bladder and rectum and the
cervical ganglia in the region of the neck. In addition,
small intermediate ganglia lie outside the conventional
vertebral chain, especially in the thoracolumbar region.
They are variable in number and location but usually
are in close proximity to the communicating rami and
the anterior spinal nerve roots.
Preganglionic fibers issuing from the spinal cord
may synapse with the neurons of more than one sympathetic
ganglion. Their principal ganglia of termination
need not correspond to the original level from which
the preganglionic fiber exits the spinal cord. Many of
the preganglionic fibers from the fifth to the last
thoracic segment pass through the paravertebral ganglia
to form the splanchnic nerves. Most of the splanchnic
nerve fibers do not synapse until they reach the
celiac ganglion; others directly innervate the adrenal
medulla (see following discussion).
Postganglionic fibers arising from sympathetic
ganglia innervate visceral structures of the thorax,
abdomen, head, and neck. The trunk and the limbs are
supplied by the sympathetic fibers in spinal nerves,
as described earlier. The prevertebral ganglia contain
cell bodies whose axons innervate the glands and
smooth muscles of the abdominal and the pelvic viscera.
Many of the upper thoracic sympathetic fibers
from the vertebral ganglia form terminal plexuses,
such as the cardiac, esophageal, and pulmonary
SECTION II
NEUROPHARMACOLOGY
plexuses. The sympathetic distribution to the head
and the neck (vasomotor, pupillodilator, secretory,
and pilomotor) is by means of the cervical sympathetic
chain and its three ganglia. All postganglionic
fibers in this chain arise from cell bodies located in
these three ganglia; all preganglionic fibers arise from
the upper thoracic segments of the spinal cord, there
being no sympathetic fibers that leave the CNS above
the first thoracic level.
The adrenal medulla and other chromaffin tissue
are embryologically and anatomically similar to sympathetic
ganglia; all are derived from the neural crest.
The adrenal medulla in humans and many other species
differs from sympathetic ganglia in that its principal
catecholamine is epinephrine (adrenaline), whereas
norepinephrine is released from postganglionic sympathetic
fibers. The chromaffin cells in the adrenal
medulla are innervated by typical preganglionic fibers
that release ACh.
Parasympathetic Nervous System. The parasympathetic
nervous system consists of preganglionic fibers that originate
in the CNS and their postganglionic connections.
The regions of central origin are the midbrain, the
medulla oblongata, and the sacral part of the spinal cord.
The midbrain, or tectal, outflow consists of fibers arising
from the Edinger-Westphal nucleus of the third cranial
nerve and going to the ciliary ganglion in the orbit. The
medullary outflow consists of the parasympathetic components
of the seventh, ninth, and tenth cranial nerves.
The fibers in the seventh (facial) cranial nerve form the
chorda tympani, which innervates the ganglia lying on the
submaxillary and sublingual glands. They also form
the greater superficial petrosal nerve, which innervates
the sphenopalatine ganglion. The autonomic components
of the ninth (glossopharyngeal) cranial nerve innervate
the otic ganglia. Postganglionic parasympathetic fibers
from these ganglia supply the sphincter of the iris (pupillary
constrictor muscle), the ciliary muscle, the salivary
and lacrimal glands, and the mucous glands of the nose,
mouth, and pharynx. These fibers also include vasodilator
nerves to these same organs. The tenth (vagus) cranial
nerve arises in the medulla and contains preganglionic
fibers, most of which do not synapse until they reach the
many small ganglia lying directly on or in the viscera of
the thorax and abdomen. In the intestinal wall, the vagal
fibers terminate around ganglion cells in the myenteric
and submucosal plexuses. Thus, in the parasympathetic
branch of the autonomic nervous system, preganglionic
fibers are very long, whereas postganglionic fibers are
very short. The vagus nerve also carries a far greater